The present invention relates to surgically implantable joint prostheses and more particularly is directed toward a joint prosthesis suitable for skeletal joints in juvenile patients which provides for adjustment as the patient grows.
Various types of surgically implantable prostheses are available as substitutes for natural skeletal joints which have become damaged by disease or trauma. Substitution by excision of the natural joint and replacement with a prosthesis is now common in connection with virtually all joints in the limbs, including toes, ankles, knees, hips, fingers, wrists, elbows and shoulders. Generally, prostheses for such purposes, particularly in the larger joints, include some type of fixation means for anchoring the prosthetic joint parts into adjacent bone. U.S. Pat. No. 4,384,373 to Sivash even shows an entire thigh bone insert having a hip joint at one end and a knee joint at the other, the prosthesis being composed of telescoping parts to allow adjustment of length at the time of implantation.
A problem exists, however, with presently available prostheses in the case of juvenile patients. As the patient grows, the limb having the prosthesis implanted typically does not grow at the same rate as the opposing limb. If the prosthesis is implanted in the knee, for example, it is common to find one leg shorter than the other. While some physical relief can be obtained with special shoes, for example, there are often psychological implications to the patient which it would be desirable to avoid. Even in adult patients it is occasionally found that due to inability to provide an implant having the exact dimension necessary to precisely replace a damaged joint or due to inaccuracies inherent in surgery adjustment of the length of the implant after the initial surgery would be desirable.